Studies will be done to investigate various aspects of the role of the kidney in hypertension: 1) The intrarenal concentration of prostaglandin E2 and F2 will be measured in rats on a low Na intake and in rats with spontaneous hypertension and "post-salt" hypertension. 2) Utilizing isolated kidneys from rats with spontaneous hypertension and "post-salt" hypertension perfused at varying inflow pressures, the output of renin, the urinary output of Na, water, and kallikrein, the intrarenal concentrations of prostaglandins E and F, and the Na reabsorption in the collecting duct will all be measured at different inflow pressures. These studies will indicate whether or not there is a "re-setting" of the hypertensive kidney, such that at normal inflow pressures it has grossly abnormal outputs of renin, Na, kallikrein, and PGE2 and abnormal reabsorption of Na in the collecting duct. Autoregulation of blood flow at varying inflow pressures will also be studied in normotensive and hypertensive kidneys. 3) Single-nephron pressures, flows, resistances will be determined at various segments along the renal vasculature in spontaneously hypertensive rats. Pressures in surface proximal and distal tubules as well as single- nephron GFR and filtration fraction will also be determined. In baby SHR rats, pressures in capillaries and loops of Henle in the papilla will also be measured. 4) The separate effects of hydrostatic pressure, osmolality, Na concentration, angiotensin, bradykinin, and anoxia on the release of E2 and F2 prostaglandins from renal papilla halves suspended in Krebs' solution in vitro will be investigated. 5) The cardiac output response to normal and high NaCl intakes will be studied in strains of rats that are either highly sensitive or highly resistant to NaCL hypertension. It is hoped that these studies will advance our understanding of the pathogenesis of chronic arterial hypertension and how the kidney relates to it.